Proper development of the nervous system relies on mechanisms to induce neuronal differntiation and to establish specific neural pathways by specifying appropriate synaptic connections between subpopulation of neurons. As a step toward understanding these processes, this project will examine the functional and structural differentiation of the two types of principal neurons in bullfrog (Rana catesbiana) sympathetic ganglia during development in vivo. Lumbar sympathetic ganglia of the frog have two identifiable classes of principal neurons, B and C cells, that are selectively innervated by two distinct populations of preganglionic axons, B and C fibers. Also, in the adult frog, the kinetic properties of the nicotinic synaptic channels of B cells differ from those of C cells. Furthermore, recent findings indicate that the expression of synaptic channel properties in reinnervated adult ganglia depends on the type of preganglionic axon innervating these neurons. This specification of synaptic channels by a reinnervating axon raises the question: Is the developmental specification of the sympathetic neuronal phenotype determined by interaction with a corresponding type of preganglionic nerve fiber? The specific aims of this proposal are: (1) to examine the development of synaptic channel properties in B and C neurons; (2) determine the influence of the preganglionic axon on the expression of synaptic channel properties during development; (3) characterize the specificity of monoclonal antibodies which are known to selectively label subsets of sympathetic neurons; (4) use these antibodies as specific markers to follow the differentiation of B and C neurons; (5) test the hypothesis that the neurons are specified as B or C according to the type of innervating preganglionic axon.